Chemistry:Psilocybin

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Short description: Chemical compound found in some species of mushrooms
Template:Chembox Dependence liability
Psilocybin
Kekulé, skeletal formula of canonical psilocybin
Spacefill model of canonical psilocybin
Names
Preferred IUPAC name
3-[2-(Dimethylamino)ethyl]-1H-indol-4-yl dihydrogen phosphate
Identifiers
3D model (JSmol)
273158
ChEBI
ChEMBL
ChemSpider
EC Number
  • 208-294-4
KEGG
MeSH Psilocybine
RTECS number
  • NM3150000
UNII
Pharmacology
Oral, intravenous
Pharmacokinetics:
Hepatic
Oral: 163±64 min
Intravenous: 74.1±19.6 min[1]
Renal
Legal status
Properties
C12H17N2O4P
Molar mass 284.252 g·mol−1
Melting point 220–228 °C (428–442 °F)[2]
Soluble
Solubility Soluble in boiling methanol and water
slightly soluble in ethanol
insoluble in chloroform, benzene[3]
Hazards
Lethal dose or concentration (LD, LC):
285 mg/kg (mouse, i.v.)
280 mg/kg (rat, i.v.)
12.5 mg/kg (rabbit, i.v.)[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Psilocybin[lower-alpha 1] (/ˌsaɪləˈsaɪbɪn/ sy-lə-SY-bin, /ˌsɪl-/) is a naturally occurring psychedelic prodrug compound produced by more than 200 species of fungi. The most potent are members of genus Psilocybe, such as P. azurescens, P. semilanceata, and P. cyanescens, but psilocybin has also been isolated from about a dozen other genera. Psilocybin is itself biologically inactive but is quickly converted by the body to psilocin, which has mind-altering effects similar, in some aspects, to those of lysergic acid diethylamide (LSD), mescaline, and dimethyltryptamine (DMT). In general, the effects include euphoria, visual and mental hallucinations, changes in perception, distorted sense of time, and perceived spiritual experiences. It can also cause adverse reactions such as nausea and panic attacks.

Imagery found on cave paintings and rock art of modern-day Spain and Algeria suggests that human use of psilocybin mushrooms predates recorded history. In Mesoamerica, the mushrooms had long been consumed in spiritual and divinatory ceremonies before Spanish chroniclers first documented their use in the sixteenth century. In 1958, the Swiss chemist Albert Hofmann isolated psilocybin and psilocin from the mushroom Psilocybe mexicana. Hofmann's employer Sandoz marketed and sold pure psilocybin to physicians and clinicians worldwide for use in psychedelic therapy. Although the increasingly restrictive drug laws of the 1960s and the 1970s curbed scientific research into the effects of psilocybin and other hallucinogens, its popularity as an entheogen (spirituality-enhancing agent) grew in the next decade, owing largely to the increased availability of information on how to cultivate psilocybin mushrooms.

The intensity and duration of the effects of psilocybin are variable, depending on species or cultivar of mushrooms, dosage, individual physiology, and set and setting, as was shown in experiments led by Timothy Leary at Harvard University in the early 1960s. Once ingested, psilocybin is rapidly metabolized to psilocin, which then acts on serotonin receptors in the brain. The mind-altering effects of psilocybin typically last from two to six hours, although to individuals under the influence of psilocybin, the effects may seem to last much longer, since the drug can distort the perception of time. Possession of psilocybin-containing mushrooms has been outlawed in most countries, and psilocybin has been classified as a Schedule I controlled substance under the 1971 United Nations Convention on Psychotropic Substances.


Effects

American psychologist and counterculture figure Timothy Leary conducted early experiments into the effects of psychedelic drugs, including psilocybin (1989 photo)

The effects of psilocybin are highly variable and depend on the mindset and environment in which the user has the experience, factors commonly referred to as set and setting. In the early 1960s, Timothy Leary and colleagues at Harvard University investigated the role of set and setting on the effects of psilocybin. They administered the drug to 175 volunteers from various backgrounds in an environment intended to be similar to a comfortable living room. 98 of the subjects were given questionnaires to assess their experiences and the contribution of background and situational factors. Individuals who had experience with psilocybin prior to the study reported more pleasant experiences than those for whom the drug was novel. Group size, dosage, preparation, and expectancy were important determinants of the drug response. In general, those in groups of more than eight felt that the groups were less supportive, and their experiences less pleasant. Conversely, smaller groups (fewer than six) were seen as more supportive and reported more positive reactions to the drug in those groups. Leary and colleagues proposed that psilocybin heightens suggestibility, making an individual more receptive to interpersonal interactions and environmental stimuli.[5] These findings were affirmed in a later review by Jos ten Berge (1999), who concluded that dosage, set, and setting were fundamental factors in determining the outcome of experiments that tested the effects of psychedelic drugs on artists' creativity.[6]

After ingesting psilocybin, a wide range of subjective effects may be experienced: feelings of disorientation, lethargy, giddiness, euphoria, joy, and depression. In one study, 31% of volunteers given a high dose reported feelings of significant fear and 17% experienced transient paranoia.[7] In studies at Johns Hopkins among those given a moderate dose (but still enough to "give a high probability of a profound and beneficial experience"), negative experiences were rare, whereas one-third of those given a high dose experienced anxiety or paranoia.[8][9] Low doses can induce hallucinatory effects. Closed-eye hallucinations may occur, where the affected individual sees multicolored geometric shapes and vivid imaginative sequences.[10] Some individuals report synesthesia, such as tactile sensations when viewing colors.[11]:175 At higher doses, psilocybin can lead to "intensification of affective responses, enhanced ability for introspection, regression to primitive and childlike thinking, and activation of vivid memory traces with pronounced emotional undertones".[12] Open-eye visual hallucinations are common, and may be very detailed although rarely confused with reality.[10]

A 2011 prospective study by Roland R. Griffiths and colleagues suggests that a single high dosage of psilocybin can cause long-term changes in the personality of its users. About half of the study participants—described as healthy, "spiritually active", and many possessing postgraduate degrees—showed an increase in the personality dimension of openness (assessed using the Revised NEO Personality Inventory), and this positive effect was apparent more than a year after the psilocybin session. According to the study authors, the finding is significant because "no study has prospectively demonstrated personality change in healthy adults after an experimentally manipulated discrete event".[13] A further study by Griffiths in 2017 found that doses of 20 to 30 mg/70 kg psilocybin inducing mystical-type experiences brought more lasting changes to traits including altruism, gratitude, forgiveness and feeling close to others when they were combined with a regular meditation practice and an extensive spiritual practice support program.[14][15] Although other researchers have described instances of psychedelic drug usage leading to new psychological understandings and personal insights,[16] it is not known whether these experimental results can be generalized to larger populations.[13]

Physical effects

Common responses include pupil dilation (93%); changes in heart rate (100%), including increases (56%), decreases (13%), and variable responses (31%); changes in blood pressure (84%), including hypotension (34%), hypertension (28%), and general instability (22%); changes in stretch reflex (86%), including increases (80%) and decreases (6%); nausea (44%); tremor (25%); and dysmetria (16%) (inability to properly direct or limit motions).[lower-alpha 2] The temporary increases in blood pressure caused by the drug can be a risk factor for users with pre-existing hypertension.[10] These qualitative somatic effects caused by psilocybin have been corroborated by several early clinical studies.[18] A 2005 magazine survey of clubgoers in the UK found that nausea or vomiting was experienced by over a quarter of those who had used psilocybin mushrooms in the last year, although this effect is caused by the mushroom rather than psilocybin itself.[7] In one study, administration of gradually increasing dosages of psilocybin daily for 21 days had no measurable effect on electrolyte levels, blood sugar levels, or liver toxicity tests.[1]

Perceptual distortions

The ability of psilocybin to cause perceptual distortions is linked to its influence on the activity of the prefrontal cortex

Psilocybin is known to strongly influence the subjective experience of the passage of time.[19] Users often feel as if time is slowed down, resulting in the perception that "minutes appear to be hours" or "time is standing still".[20] Studies have demonstrated that psilocybin significantly impairs subjects' ability to gauge time intervals longer than 2.5 seconds, impairs their ability to synchronize to inter-beat intervals longer than 2 seconds, and reduces their preferred tapping rate.[20][21] These results are consistent with the drug's role in affecting prefrontal cortex activity,[22] and the role that the prefrontal cortex is known to play in time perception.[23] However, the neurochemical basis of psilocybin's effects on the perception of time are not known with certainty.[24]

Users having a pleasant experience can feel a sense of connection to others, nature, and the universe; other perceptions and emotions are also often intensified. Users having an unpleasant experience (a "bad trip") describe a reaction accompanied by fear, other unpleasant feelings, and occasionally by dangerous behavior. In general, the phrase "bad trip" is used to describe a reaction that is characterized primarily by fear or other unpleasant emotions, not just transitory experience of such feelings. A variety of factors may contribute to a psilocybin user experiencing a bad trip, including "tripping" during an emotional or physical low or in a non-supportive environment (see: set and setting). Ingesting psilocybin in combination with other drugs, including alcohol, can also increase the likelihood of a bad trip.[7][25] Other than the duration of the experience, the effects of psilocybin are similar to comparable dosages of lysergic acid diethylamide (LSD) or mescaline. However, in the Psychedelics Encyclopedia, author Peter Stafford noted, "The psilocybin experience seems to be warmer, not as forceful and less isolating. It tends to build connections between people, who are generally much more in communication than when they use LSD."[26]:273

Group perceptions

Through further anthropological studies regarding "personal insights"[27] and the psycho-social effects of psilocybin, it can be seen in many traditional societies that powerful mind-active substances such as psilocybin are regularly "consumed ritually for therapeutic purposes or for transcending normal, everyday reality".[28] Positive effects that psilocybin has on individuals can be observed by taking on an anthropological approach and moving away from the Western bio-medical society; this is aided by the studies done by Leary.[29] Within certain traditional societies where the use of psilocybin is frequent for shamanic healing rituals, group collectives praise their guide, healer and shaman for helping alleviate them of pains, aches and hurt. They do this through a group ritual practice where participants, or just the guide, ingests psilocybin to help extract any "toxic psychic residues or sorcerous implants"[28] found in one's body. Group therapies using classic psychedelics are becoming more commonly used in the Western world in clinical practice. This may continue to grow as long providing the evidence remains indicative of safety and efficacy.[30] In social sense, the group is shaped by their experiences surrounding psilocybin and how they view the plant collectively. As mentioned in the anthropology article,[28] the group partakes in a "journey" together, thus adding to the spiritual, social body, where roles, hierarchies and gender are subjectively understood.[28]

Mystical experiences

In their studies on the psilocybin experience, Johns Hopkins researchers use peaceful music and a comfortable room to help ensure a comfortable setting, and experienced guides to monitor and reassure the volunteers

Psilocybin mushrooms have been and continue to be used in indigenous New World cultures in religious, divinatory, or spiritual contexts. Reflecting the meaning of the word entheogen ("the god within"), the mushrooms are revered as powerful spiritual sacraments that provide access to sacred worlds. Typically used in small group community settings, they enhance group cohesion and reaffirm traditional values.[31] Terence McKenna documented the worldwide practices of psilocybin mushroom usage as part of a cultural ethos relating to the Earth and mysteries of nature, and suggested that mushrooms enhanced self-awareness and a sense of contact with a "Transcendent Other"—reflecting a deeper understanding of our connectedness with nature.[32]

Psychedelic drugs can induce states of consciousness that have lasting personal meaning and spiritual significance in individuals who are religious or spiritually inclined; these states are called mystical experiences. Some scholars have proposed that many of the qualities of a drug-induced mystical experience are indistinguishable from mystical experiences achieved through non-drug techniques, such as meditation or holotropic breathwork.[33][34] In the 1960s, Walter Pahnke and colleagues systematically evaluated mystical experiences (which they called "mystical consciousness") by categorizing their common features. These categories, according to Pahnke, "describe the core of a universal psychological experience, free from culturally determined philosophical or theological interpretations", and allow researchers to assess mystical experiences on a qualitative, numerical scale.[35]

In the 1962 Marsh Chapel Experiment, which was run by Pahnke at the Harvard Divinity School under the supervision of Timothy Leary,[36] almost all of the graduate degree divinity student volunteers who received psilocybin reported profound religious experiences.[37] One of the participants was religious scholar Huston Smith, author of several textbooks on comparative religion; he later described his experience as "the most powerful cosmic homecoming I have ever experienced."[38] In a 25-year followup to the experiment, all of the subjects given psilocybin described their experience as having elements of "a genuine mystical nature and characterized it as one of the high points of their spiritual life".[39]:13 Psychedelic researcher Rick Doblin considered the study partially flawed due to incorrect implementation of the double-blind procedure, and several imprecise questions in the mystical experience questionnaire. Nevertheless, he said that the study cast "a considerable doubt on the assertion that mystical experiences catalyzed by drugs are in any way inferior to non-drug mystical experiences in both their immediate content and long-term effects".[39]:24 This sentiment was echoed by psychiatrist William A. Richards, who in a 2007 review stated "[psychedelic] mushroom use may constitute one technology for evoking revelatory experiences that are similar, if not identical, to those that occur through so-called spontaneous alterations of brain chemistry."[40]

A group of researchers from Johns Hopkins School of Medicine led by Roland Griffiths conducted a study to assess the immediate and long-term psychological effects of the psilocybin experience, using a modified version of the mystical experience questionnaire and a rigorous double-blind procedure.[41] When asked in an interview about the similarity of his work with Leary's, Griffiths explained the difference: "We are conducting rigorous, systematic research with psilocybin under carefully monitored conditions, a route which Dr. Leary abandoned in the early 1960s."[42] The National Institute of Drug Abuse-funded study, published in 2006, has been praised by experts for the soundness of its experimental design.[lower-alpha 3] In the experiment, 36 volunteers without prior experience with hallucinogens were given psilocybin and methylphenidate (Ritalin) in separate sessions; the methylphenidate sessions served as a control and psychoactive placebo. The degree of mystical experience was measured using a questionnaire developed by Ralph W. Hood;[43] 61% of subjects reported a "complete mystical experience" after their psilocybin session, while only 13% reported such an outcome after their experience with methylphenidate. Two months after taking psilocybin, 79% of the participants reported moderately to greatly increased life satisfaction and sense of well-being. About 36% of participants also had a strong to extreme "experience of fear" or dysphoria (i.e., a "bad trip") at some point during the psilocybin session (which was not reported by any subject during the methylphenidate session); about one-third of these (13% of the total) reported that this dysphoria dominated the entire session. These negative effects were reported to be easily managed by the researchers and did not have a lasting negative effect on the subject's sense of well-being.[44]

A follow-up study conducted 14 months after the original psilocybin session confirmed that participants continued to attribute deep personal meaning to the experience. Almost one-third of the subjects reported that the experience was the single most meaningful or spiritually significant event of their lives, and over two-thirds reported it among their five most spiritually significant events. About two-thirds indicated that the experience increased their sense of well-being or life satisfaction.[37] Even after 14 months, those who reported mystical experiences scored on average 4 percentage points higher on the personality trait of Openness/Intellect; personality traits are normally stable across the lifespan for adults. Likewise, in a recent (2010) web-based questionnaire study designed to investigate user perceptions of the benefits and harms of hallucinogenic drug use, 60% of the 503 psilocybin users reported that their use of psilocybin had a long-term positive impact on their sense of well-being.[7][45]

While many recent studies have concluded that psilocybin can cause mystical-type experiences having substantial and sustained personal meaning and spiritual significance, not all the medical community agree. Paul R. McHugh, formerly director of the Department of Psychiatry and Behavioral Science at Johns Hopkins, responded as follows in a book review: "The unmentioned fact in The Harvard Psychedelic Club is that LSD, psilocybin, mescaline, and the like produce not a "higher consciousness" but rather a particular kind of "lower consciousness" known well to psychiatrists and neurologists—namely, 'toxic delirium.'"[46]

Available forms

Although psilocybin may be prepared synthetically, outside of the research setting it is not typically used in this form. The psilocybin present in certain species of mushrooms can be ingested in several ways: by consuming fresh or dried fruit bodies, by preparing an herbal tea, or by combining with other foods to mask the bitter taste.[47] In rare cases people have injected mushroom extracts intravenously.[7]

Adverse effects

Most of the comparatively few fatal incidents reported in the literature that are associated with psychedelic mushroom usage involve the simultaneous use of other drugs, especially alcohol. Probably the most common cause of hospital admissions resulting from psychedelic mushroom usage involves "bad trips" or panic reactions, in which affected individuals become extremely anxious, confused, agitated, or disoriented. Accidents, self-injury, or suicide attempts can result from serious cases of acute psychotic episodes.[7] Although no studies have linked psilocybin with birth defects,[48] it is recommended that pregnant women avoid its usage.[49]

Toxicity

Data are sparse, but in the decade leading up to 2020, an increasing number of psilocybin mushroom overdoses were recorded. Nonetheless, the number of events requiring hospitalization remain rare, and overdoses are generally mild and self-limiting. A review regarding the management of psychedelic overdoses suggested that psilocybin related overdose management should prioritize managing the immediate adverse effects, such as anxiety and paranoia, rather than specific pharmacological interventions, as its physiological toxicity tends to be rather limited.[50] One analysis of mushrooms used by people hospitalized from psilocybin poisoning found high concentrations of phenethylamine (PEA), which has also been detected in the urine of people who have used psilocybin mushrooms. It is hypothesized that PEA may intensify the effect of psilocybin poisoning.[50]

In rats, the median lethal dose (LD50) when administered orally is 280 milligrams per kilogram (mg/kg), approximately one and a half times that of caffeine. When administered intravenously in rabbits, psilocybin's LD50 is approximately 12.5 mg/kg.[51] Psilocybin comprises approximately 1% of the weight of Psilocybe cubensis mushrooms, and so nearly 1.7 kilograms (3.7 lb) of dried mushrooms, or 17 kilograms (37 lb) of fresh mushrooms, would be required for a 60-kilogram (130 lb) person to reach the 280 mg/kg LD50 value of rats.[7] Based on the results of animal studies, the lethal dose of psilocybin has been extrapolated to be 6 grams, 1000 times greater than the effective dose of 6 milligrams.[52] The Registry of Toxic Effects of Chemical Substances assigns psilocybin a relatively high therapeutic index of 641 (higher values correspond to a better safety profile); for comparison, the therapeutic indices of aspirin and nicotine are 199 and 21, respectively.[53] The lethal dose from psilocybin toxicity alone is unknown, and has rarely been documented—(As of 2011), only two cases attributed to overdosing on hallucinogenic mushrooms (without concurrent use of other drugs) have been reported in the scientific literature and may involve other factors aside from psilocybin.[7][lower-alpha 4]

Psychiatric

Panic reactions can occur after consumption of psilocybin-containing mushrooms, especially if the ingestion is accidental or otherwise unexpected. Reactions characterized by violent behavior, suicidal thoughts,[56] schizophrenia-like psychosis,[57][58] and convulsions[59] have been reported in the literature. A 2005 survey conducted in the United Kingdom found that almost a quarter of those who had used psilocybin mushrooms in the past year had experienced a panic attack.[7] [failed verification] Other adverse effects less frequently reported include paranoia, confusion, prolonged derealization (disconnection from reality), and mania.[45] Psilocybin usage can temporarily induce a state of depersonalization disorder.[60] Usage by those with schizophrenia can induce acute psychotic states requiring hospitalization.[61]

The similarity of psilocybin-induced symptoms to those of schizophrenia has made the drug a useful research tool in behavioral and neuroimaging studies of this psychotic disorder.[62][63][64] In both cases, psychotic symptoms are thought to arise from a "deficient gating of sensory and cognitive information" in the brain that ultimately lead to "cognitive fragmentation and psychosis".[63] Flashbacks (spontaneous recurrences of a previous psilocybin experience) can occur long after having used psilocybin mushrooms. Hallucinogen persisting perception disorder (HPPD) is characterized by a continual presence of visual disturbances similar to those generated by psychedelic substances. Neither flashbacks nor HPPD are commonly associated with psilocybin usage,[7] and correlations between HPPD and psychedelics are further obscured by polydrug use and other variables.[65]

Tolerance and dependence

Chart of dependence potential and effective dose/lethal dose ratio of several psychoactive drugs[66]

Tolerance to psilocybin builds and dissipates quickly; ingesting psilocybin more than about once a week can lead to diminished effects. Tolerance dissipates after a few days, so doses can be spaced several days apart to avoid the effect.[67] A cross-tolerance can develop between psilocybin and the pharmacologically similar LSD,[68] and between psilocybin and phenethylamines such as mescaline and DOM.[69]

Repeated use of psilocybin does not lead to physical dependence.[1] A 2008 study concluded that, based on US data from the period 2000–2002, adolescent-onset (defined here as ages 11–17) usage of hallucinogenic drugs (including psilocybin) did not increase the risk of drug dependence in adulthood; this was in contrast to adolescent usage of cannabis, cocaine, inhalants, anxiolytic medicines, and stimulants, all of which were associated with "an excess risk of developing clinical features associated with drug dependence".[70] Likewise, a 2010 Dutch study ranked the relative harm of psilocybin mushrooms compared to a selection of 19 recreational drugs, including alcohol, cannabis, cocaine, ecstasy, heroin, and tobacco. Psilocybin mushrooms were ranked as the illicit drug with the lowest harm,[71] corroborating conclusions reached earlier by expert groups in the United Kingdom.[72]

Chemistry

Physical properties

Psilocybin is a naturally-occurring substituted tryptamine that features an indole ring linked to an aminoethyl substituent. It is structurally related to serotonin, a monoamine neurotransmitter which is a derivative of the amino acid tryptophan. Psilocybin is a member of the general class of tryptophan-based compounds that originally functioned as antioxidants in earlier life forms before assuming more complex functions in multicellular organisms, including humans.[73] Other related indole-containing psychedelic compounds include dimethyltryptamine, found in many plant species and in trace amounts in some mammals, and bufotenin, found in the skin of certain amphibians, especially the Colorado River toad.[74]:10–13

Psilocybin is a white, crystalline solid that is soluble in water, methanol and ethanol but insoluble in nonpolar organic solvents such as chloroform and petroleum ether.[74]:15 It has a melting point between 220–228 °C (428–442 °F),[51] and an ammonia-like taste.[75] Its pKa values are estimated to be 1.3 and 6.5 for the two successive phosphate hydroxy groups and 10.4 for the dimethylamine nitrogen, so it typically exists as a zwitterionic structure.[75] There are two known crystalline polymorphs of psilocybin, as well as reported hydrated phases.[76] Psilocybin rapidly oxidizes upon exposure to light—an important consideration when using it as an analytical standard.[77]

Laboratory synthesis

Albert Hofmann et al. were the first team to synthesize psilocybin in 1958. Since that time, various chemists have improved the methods for the laboratory synthesis and purification of psilocybin. In particular, Shirota et al. reported a novel method in 2003 for the synthesis of psilocybin at the gram scale from 4-hydroxyindole that does not require chromatographic purification. Fricke et al. described an enzymatic pathway for the synthesis of psilocybin and psilocin, publishing their results in 2017. Sherwood et al. significantly improved upon Shirota's method (producing at the kilogram scale while employing less expensive reagents), publishing their results in 2020.[78]

Biosynthesis

Biosynthetic route previously thought to lead to psilocybin. It has recently been shown that 4-hydroxylation and O-phosphorylation immediately follow decarboxylation, and neither dimethyltryptamine nor psilocin are intermediates, although spontaneously generated psilocin can be converted back to psilocybin.[79]

Isotopic labeling experiments from the 1960s suggested that the biosynthesis of psilocybin was a four-step process:[80]

  1. decarboxylation of tryptophan to tryptamine
  2. N,N-dimethylation of tryptamine at the N9 position to dimethyltryptamine
  3. 4-hydroxylation of dimethyltryptamine to psilocin
  4. O-phosphorylation of psilocin to psilocybin

More recent research has demonstrated that—at least in P. cubensis—O-phosphorylation is in fact the third step, and that neither dimethyltryptamine nor psilocin are intermediates.[79] The sequence of the intermediate steps has been shown to involve four enzymes (PsiD, PsiH, PsiK, and PsiM) in P. cubensis and P. cyanescens, although it is possible that the biosynthetic pathway differs between species.[74]:12–13[79] These enzymes are encoded in gene clusters in Psilocybe, Panaeolus, and Gymnopilus.[81]

Escherichia coli has been genetically modified to manufacture large amounts of psilocybin.[82] Psilocybin can be produced de novo in GM yeast.[83][84]

Pharmacology

Pharmacodynamics

The neurotransmitter serotonin is structurally similar to psilocybin

Psilocybin is a psychoplastogen,[85][86][87] which refers to a compound capable of promoting rapid and sustained neuroplasticity.

Psilocybin is rapidly dephosphorylated in the body to psilocin, which is an agonist for several serotonin receptors, which are also known as 5-hydroxytryptamine (5-HT) receptors. In rats, psilocin binds with high affinity to 5-HT2A receptors and low affinity to 5-HT1 receptors, including 5-HT1A and 5-HT1D; effects are also mediated via 5-HT2C receptors.[1] The psychotomimetic (psychosis-mimicking) effects of psilocin can be blocked in a dose-dependent fashion by the 5-HT2A antagonist drug ketanserin.[57] Various lines of evidence have shown that interactions with non-5-HT2 receptors also contribute to the subjective and behavioral effects of the drug.[69][lower-alpha 5] For example, psilocin indirectly increases the concentration of the neurotransmitter dopamine in the basal ganglia, and some psychotomimetic symptoms of psilocin are reduced by haloperidol, a non-selective dopamine receptor antagonist. Taken together, these suggest that there may be an indirect dopaminergic contribution to psilocin's psychotomimetic effects.[24] Psilocybin and psilocin have no affinity for dopamine receptor D2, unlike another common 5-HT receptor agonist, lysergic acid diethylamide (LSD).[1] Psilocin antagonizes H1 receptors with moderate affinity, compared to LSD which has a lower affinity.[89] Serotonin receptors are located in numerous parts of the brain, including the cerebral cortex, and are involved in a wide range of functions, including regulation of mood, motivation, body temperature, appetite and libido.[90]

Psilocybin induces region-dependent alterations in glutamate that may be associated with subjective experiences of ego dissolution.[91]

Pharmacokinetics

Psilocybin is converted in the liver to the pharmacologically active psilocin, which is then either glucuronated to be excreted in the urine or further converted to various psilocin metabolites

The effects of the drug begin 10–40 minutes after ingestion, and last 2–6 hours depending on dose, species, and individual metabolism.[92]:36–41 The half life of psilocybin is 163 ± 64 minutes when taken orally, or 74.1 ± 19.6 minutes when injected intravenously.[1]

Psilocybin is metabolized mostly in the liver. As it becomes converted to psilocin, it undergoes a first-pass effect, whereby its concentration is greatly reduced before it reaches the systemic circulation. Psilocin is broken down by the enzyme monoamine oxidase to produce several metabolites that can circulate in the blood plasma, including 4-hydroxyindole-3-acetaldehyde, 4-hydroxytryptophol, and 4-hydroxyindole-3-acetic acid.[1] Some psilocin is not broken down by enzymes and instead forms a glucuronide; this is a biochemical mechanism animals use to eliminate substances by linking them with glucuronic acid, which can then be excreted in the urine.[93][94] Psilocin is glucuronated by the glucuronosyltransferase enzymes UGT1A9 in the liver, and by UGT1A10 in the small intestine.[95] Based on studies using animals, about 50% of ingested psilocybin is absorbed through the stomach and intestine. Within 24 hours, about 65% of the absorbed psilocybin is excreted into the urine, and a further 15–20% is excreted in the bile and feces. Although most of the remaining drug is eliminated in this way within 8 hours, it is still detectable in the urine after 7 days.[96] Clinical studies show that psilocin concentrations in the plasma of adults average about 8 μg/liter within 2 hours after ingestion of a single 15 mg oral psilocybin dose;[97] psychological effects occur with a blood plasma concentration of 4–6 μg/liter.[1] Psilocybin is approximately 1/100 the potency of LSD on a weight per weight basis, and the physiological effects last about half as long.[11]:171

Monoamine oxidase inhibitors (MAOI) have been known to prolong and enhance the effects of DMT and one study assumed that the effect on psilocybin would be similar since it is a structural analogue of DMT.[98] Alcohol consumption may enhance the effects of psilocybin, because acetaldehyde, one of the primary breakdown metabolites of consumed alcohol, reacts with biogenic amines present in the body to produce MAOIs related to tetrahydroisoquinoline and β-carboline.[7] Tobacco smokers may also experience more powerful effects with psilocybin,[7] because tobacco smoke exposure decreases the activity of MAO in the brain and peripheral organs.[99]

Analytical methods

Several relatively simple chemical tests—commercially available as reagent testing kits—can be used to assess the presence of psilocybin in extracts prepared from mushrooms. The drug reacts in the Marquis test to produce a yellow color, and a green color in the Mandelin reagent.[100] Neither of these tests, however, is specific for psilocybin; for example, the Marquis test will react with many classes of controlled drugs, such as those containing primary amino groups and unsubstituted benzene rings, including amphetamine and methamphetamine.[101] Ehrlich's reagent and DMACA reagent are used as chemical sprays to detect the drug after thin layer chromatography.[102] Many modern techniques of analytical chemistry have been used to quantify psilocybin levels in mushroom samples. Although the earliest methods commonly used gas chromatography, the high temperature required to vaporize the psilocybin sample prior to analysis causes it to spontaneously lose its phosphoryl group and become psilocin—making it difficult to chemically discriminate between the two drugs. In forensic toxicology, techniques involving gas chromatography coupled to mass spectrometry (GC–MS) are the most widely used due to their high sensitivity and ability to separate compounds in complex biological mixtures.[103] These techniques include ion mobility spectrometry,[104] capillary zone electrophoresis,[105] ultraviolet spectroscopy,[106] and infrared spectroscopy.[107] High-performance liquid chromatography (HPLC) is used with ultraviolet,[77] fluorescence,[108] electrochemical,[109] and electrospray mass spectrometric detection methods.[110]

Various chromatographic methods have been developed to detect psilocin in body fluids: the rapid emergency drug identification system (REMEDi HS), a drug screening method based on HPLC;[111] HPLC with electrochemical detection;[109][112] GC–MS;[93][111] and liquid chromatography coupled to mass spectrometry.[113] Although the determination of psilocin levels in urine can be performed without sample clean-up (i.e., removing potential contaminants that make it difficult to accurately assess concentration), the analysis in plasma or serum requires a preliminary extraction, followed by derivatization of the extracts in the case of GC–MS. A specific immunoassay has also been developed to detect psilocin in whole blood samples.[114] A 2009 publication reported using HPLC to quickly separate forensically important illicit drugs including psilocybin and psilocin, which were identifiable within about half a minute of analysis time.[115] These analytical techniques to determine psilocybin concentrations in body fluids are, however, not routinely available, and not typically used in clinical settings.[25]

Natural occurrence

Maximum reported psilocybin concentrations (% dry weight) in 12 Psilocybe species[92]:39
Species % psilocybin
P. azurescens 1.78
P. serbica 1.34
P. semilanceata 0.98
P. baeocystis 0.85
P. cyanescens 0.85
P. tampanensis 0.68
P. cubensis 0.63
P. weilii 0.61
P. hoogshagenii 0.60
P. stuntzii 0.36
P. cyanofibrillosa 0.21
P. liniformans 0.16

Psilocybin is present in varying concentrations in over 200 species of Basidiomycota mushrooms. In a 2000 review on the worldwide distribution of hallucinogenic mushrooms, Gastón Guzmán and colleagues considered these to be distributed amongst the following genera: Psilocybe (116 species), Gymnopilus (14), Panaeolus (13), Copelandia (12), Hypholoma (6), Pluteus (6), Inocybe (6), Conocybe (4), Panaeolina (4), Gerronema (2), and Galerina (1 species).[116] Guzmán increased his estimate of the number of psilocybin-containing Psilocybe to 144 species in a 2005 review. The majority of these are found in Mexico (53 species), with the remainder distributed in the United States and Canada (22), Europe (16), Asia (15), Africa (4), and Australia and associated islands (19).[117] The diversity of psilocybin mushrooms is reported to have been increased by horizontal transfer of the psilocybin gene cluster between unrelated mushroom species.[118][81] In general, psilocybin-containing species are dark-spored, gilled mushrooms that grow in meadows and woods of the subtropics and tropics, usually in soils rich in humus and plant debris.[74]:5 Psilocybin mushrooms occur on all continents, but the majority of species are found in subtropical humid forests.[116] Psilocybe species commonly found in the tropics include P. cubensis and P. subcubensis. P. semilanceata—considered by Guzmán to be the world's most widely distributed psilocybin mushroom[119]—is found in Europe, North America, Asia, South America, Australia and New Zealand, but is entirely absent from Mexico.[117] Although the presence or absence of psilocybin is not of much use as a chemotaxonomical marker at the familial level or higher, it is used to classify taxa of lower taxonomic groups.[120]

Global distribution of over 100 psychoactive species of genus Psilocybe mushrooms.[121]
The mushroom Psilocybe mexicana
Psilocybin was first isolated from Psilocybe mexicana.
The mushroom Psilocybe semilanceata
P. semilanceata is common in Europe, Canada, and the United States.

Both the caps and the stems contain psychoactive compounds, although the caps consistently contain more. The spores of these mushrooms do not contain psilocybin or psilocin.[104][122][123] The total potency varies greatly between species and even between specimens of a species collected or grown from the same strain.[124] Because most psilocybin biosynthesis occurs early in the formation of fruit bodies or sclerotia, younger, smaller mushrooms tend to have a higher concentration of the drug than larger, mature mushrooms.[125] In general, the psilocybin content of mushrooms is quite variable (ranging from almost nothing to 2.5% of the dry weight)[126][26]:248 and depends on species, strain, growth and drying conditions, and mushroom size.[92]:36–41, 52 Cultivated mushrooms have less variability in psilocybin content than wild mushrooms.[127] The drug is more stable in dried than fresh mushrooms; dried mushrooms retain their potency for months or even years,[92]:51–5 while mushrooms stored fresh for four weeks contain only traces of the original psilocybin.[7]

The psilocybin contents of dried herbarium specimens of Psilocybe semilanceata in one study were shown to decrease with the increasing age of the sample: collections dated 11, 33, or 118 years old contained 0.84%, 0.67%, and 0.014% (all dry weight), respectively.[128] Mature mycelia contain some psilocybin, while young mycelia (recently germinated from spores) lack appreciable amounts.[129] Many species of mushrooms containing psilocybin also contain lesser amounts of the analog compounds baeocystin and norbaeocystin,[92]:38 chemicals thought to be biogenic precursors.[11]:170 Although most species of psilocybin-containing mushrooms bruise blue when handled or damaged due to the oxidization of phenolic compounds, this reaction is not a definitive method of identification or determining a mushroom's potency.[124][92]:56–58

History

Early

Mayan "mushroom stones" of Guatemala

There is evidence to suggest that psychoactive mushrooms have been used by humans in religious ceremonies for thousands of years. 6,000-year-old pictographs discovered near the Spanish town of Villar del Humo illustrate several mushrooms that have been tentatively identified as Psilocybe hispanica, a hallucinogenic species native to the area.[130] The rock art was also discovered in Tassili, Algeria, and is believed to depict psychedelic mushrooms and the transformation of the user under their influence. The paintings are said to date back to 9000-7000 BC.[131] Archaeological artifacts from Mexico, as well as the so-called Mayan "mushroom stones" of Guatemala have also been interpreted by some scholars as evidence for ritual and ceremonial usage of psychoactive mushrooms in the Mayan and Aztec cultures of Mesoamerica.[92]:11 In Nahuatl, the language of the Aztecs, the mushrooms were called teonanácatl, or "God's flesh". Following the arrival of Spanish explorers to the New World in the sixteenth century, chroniclers reported the use of mushrooms by the natives for ceremonial and religious purposes. According to the Dominican friar Diego Durán in The History of the Indies of New Spain (published c. 1581), mushrooms were eaten in festivities conducted on the occasion of the accession to the throne of Aztec emperor Moctezuma II in 1502. The Franciscan friar Bernardino de Sahagún wrote of witnessing mushroom usage in his Florentine Codex (published 1545–1590),[132]:164 and described how some merchants would celebrate upon returning from a successful business trip by consuming mushrooms to evoke revelatory visions.[133]:118 After the defeat of the Aztecs, the Spanish forbade traditional religious practices and rituals that they considered "pagan idolatry", including ceremonial mushroom use. For the next four centuries, the Indians of Mesoamerica hid their use of entheogens from the Spanish authorities.[132]:165

Although dozens of species of psychedelic mushrooms are found in Europe, there is little documented usage of these species in Old World history besides the use of Amanita muscaria among Siberian peoples.[134][135] The few existing historical accounts about psilocybin mushrooms typically lack sufficient information to allow species identification, and usually refer to the nature of their effects. For example, Flemish botanist Carolus Clusius (1526–1609) described the bolond gomba (crazy mushroom), used in rural Hungary to prepare love potions. English botanist John Parkinson included details about a "foolish mushroom" in his 1640 herbal Theatricum Botanicum.[136]:10–12 The first reliably documented report of intoxication with Psilocybe semilanceata—Europe's most common and widespread psychedelic mushroom—involved a British family in 1799, who prepared a meal with mushrooms they had picked in London's Green Park.[136]:16

Modern

Albert Hofmann (shown here in 1993) purified psilocybin and psilocin from Psilocybe mexicana in the late 1950s
The increasing availability of information on growing techniques made it possible for amateurs to grow psilocybin mushrooms (Psilocybe cubensis pictured) without access to laboratory equipment

American banker and amateur ethnomycologist R. Gordon Wasson and his wife Valentina P. Wasson, a physician, studied the ritual use of psychoactive mushrooms by the native population in the Mazatec village Huautla de Jiménez, Mexico. In 1957, Wasson described the psychedelic visions that he experienced during these rituals in "Seeking the Magic Mushroom", an article published in the popular American weekly Life magazine.[137] Later the same year they were accompanied on a follow-up expedition by French mycologist Roger Heim, who identified several of the mushrooms as Psilocybe species.[138]

Heim cultivated the mushrooms in France and sent samples for analysis to Albert Hofmann, a chemist employed by the Swiss pharmaceutical company Sandoz (now Novartis). Hofmann—who had synthesized lysergic acid diethylamide (LSD) in 1938—led a research group that isolated and identified the psychoactive alkaloids psilocybin and psilocin from Psilocybe mexicana, publishing their results in 1958.[133]:128 The team was aided in the discovery process by Hofmann's willingness to ingest mushroom extracts to help verify the presence of the active compounds.[133]:126–127

Next, Hofmann's team synthesized several structural analogs of these compounds to examine how these structural changes would affect psychoactivity. This research led to the development of ethocybin and CZ-74. Because the physiological effects of these compounds last only about three and a half hours (about half as long as psilocybin), they proved more manageable than the latter for use in psycholytic therapy.[26]:237 Sandoz also marketed and sold pure psilocybin under the name Indocybin to clinicians and researchers worldwide.[132]:166 There were no reports of serious complications when psilocybin was used in this way.[1]

In the early 1960s, Harvard University became a testing ground for psilocybin, through the efforts of Timothy Leary and his associates Ralph Metzner and Richard Alpert (who later changed his name to Ram Dass). Leary obtained synthesized psilocybin from Hofmann through Sandoz Pharmaceuticals. Some studies, such as the Concord Prison Experiment, suggested promising results using psilocybin in clinical psychiatry.[5][139] According to a 2008 review of safety guidelines in human hallucinogenic research, however, Leary and Alpert's well-publicized termination from Harvard and later advocacy of hallucinogen use "further undermined an objective scientific approach to studying these compounds".[140] In response to concerns about the increase in unauthorized use of psychedelic drugs by the general public, psilocybin and other hallucinogenic drugs suffered negative press and faced increasingly restrictive laws. In the United States, laws were passed in 1966 that prohibited the production, trade, or ingestion of hallucinogenic drugs; Sandoz stopped producing LSD and psilocybin the same year.[96] In 1970, Congress passed "The Federal Comprehensive Drug Abuse Prevention and Control Act" that made LSD, peyote, psilocybin and other hallucinogens illegal to use for any and all purposes, including scientific research.[141] United States politicians' agenda against LSD usage had swept psilocybin along with it into the Schedule I category of illicit drugs. Such restrictions on the use of these drugs in human research made funding for such projects difficult to obtain, globally, and scientists who worked with psychedelic drugs faced being "professionally marginalized".[142] Although Hofmann tested these compounds on himself, he never advocated their legalization or medical use. In his 1979 book LSD — mein Sorgenkind ("LSD — my problem child"), Hofmann described the problematic use of these hallucinogens as inebriants.[133]:79–116

Despite the legal restrictions on psilocybin use, the 1970s witnessed the emergence of psilocybin as the "entheogen of choice".[143]:276 This was due in large part to a wide dissemination of information on the topic, which included works such as those by author Carlos Castaneda, and several books that taught the technique of growing psilocybin mushrooms. One of the most popular of this latter group was published in 1976 under the pseudonyms O.T. Oss and O.N. Oeric by Jeremy Bigwood, Dennis J. McKenna, K. Harrison McKenna, and Terence McKenna, entitled Psilocybin: Magic Mushroom Grower's Guide. Over 100,000 copies were sold by 1981.[144] As ethnobiologist Jonathan Ott explains, "These authors adapted San Antonio's technique (for producing edible mushrooms by casing mycelial cultures on a rye grain substrate; San Antonio 1971) to the production of Psilocybe [Stropharia] cubensis. The new technique involved the use of ordinary kitchen implements, and for the first time the layperson was able to produce a potent entheogen in his own home, without access to sophisticated technology, equipment or chemical supplies."[143]:290 San Antonio's technique describes a method to grow the common edible mushroom Agaricus bisporus[145]

Because of a lack of clarity about laws about psilocybin mushrooms, specifically in the form of sclerotia (also known as "truffles"), European retailers in the late 1990s and early 2000s commercialized and marketed them in smartshops in the Netherlands and the UK, and online. Several websites[lower-alpha 6] emerged that have contributed to the accessibility of information on description, use, effects and exchange of experiences among users. Since 2001, six EU countries have tightened their legislation on psilocybin mushrooms in response to concerns about their prevalence and increasing usage.[47] In the 1990s, hallucinogens and their effects on human consciousness were again the subject of scientific study, particularly in Europe. Advances in neuropharmacology and neuropsychology, and the availability of brain imaging techniques have provided impetus for using drugs like psilocybin to probe the "neural underpinnings of psychotic symptom formation including ego disorders and hallucinations".[12] Recent studies in the United States have attracted attention from the popular press and thrust psilocybin back into the limelight.[146][147]

Society and culture

Legal status

This section is an excerpt from Legal status of psilocybin mushrooms[ edit ]

Advocacy for tolerance

Despite being illegal in many typically Western countries, such as the UK, Australia and some US states, less conservative governments opt to nurture the legal use of psilocybin and other psychedelic drugs. In Amsterdam, Netherlands, authorities provide education and promotion on the safe use of psychedelic drugs, such as psilocybin, in an aim to reduce public harm.[148] Similarly, religious groups like America's Uniao do Vegetal, UDV,[149] use psychedelics in traditional ceremonies.[150] From 1 July 2023, the Australian medicines regulator has permitted psychiatrists to prescribe psilocybin for the therapeutic treatment of post-traumatic stress disorder.[151]

Advocates for legalization argue there is a lack of evidence of harm,[152][153] and potential use in treating certain mental health conditions. Research is difficult to conduct because of the legal status of psychoactive substances.[154] Advocates for legalization also promote the utility of "ego dissolution"[149] and argue bans are cultural discrimination against traditional users.[155]

Usage

Dried Psilocybe mushrooms showing the characteristic blue bruising on the stems

A 2009 national survey of drug use by the US Department of Health and Human Services concluded that the number of first-time psilocybin mushroom users in the United States was roughly equivalent to the number of first-time users of cannabis.[156] In European countries, the lifetime prevalence estimates of psychedelic mushroom usage among young adults (15–34 years) range from 0.3% to 14.1%.[157]

In modern Mexico, traditional ceremonial use survives among several indigenous groups, including the Nahuas, the Matlatzinca, the Totonacs, the Mazatecs, Mixes, Zapotecs, and the Chatino. Although hallucinogenic Psilocybe species are abundant in low-lying areas of Mexico, most ceremonial use takes places in mountainous areas of elevations greater than 1,500 meters (4,900 ft). Guzmán suggests this is a vestige of Spanish colonial influence from several hundred years earlier, when mushroom use was persecuted by the Catholic Church.[158]

Research

Psilocybin has been a subject of clinical research since the early 1960s, when the Harvard Psilocybin Project evaluated the potential value of psilocybin as a treatment for certain personality disorders.[159] Beginning in the 2000s, psilocybin has been investigated for its possible role in the treatment of nicotine dependence, alcohol dependence, obsessive–compulsive disorder (OCD), cluster headache, cancer-related existential distress[78][160] anxiety disorders, and certain mood disorders.[132]:179–81[161][162] In 2018, the United States Food and Drug Administration (FDA) granted breakthrough therapy designation for psilocybin-assisted therapy for treatment-resistant depression.[163][164] A systematic review published in 2021 found that the use of psilocybin as a pharmaceutical substance was associated with reduced intensity of depression symptoms.[165] The role of psilocybin as a possible psychoplastogen is also being examined.[85][86][87]

See also

Explanatory notes

  1. ↑ Synonyms and alternate spellings include: 4-PO-DMT (PO: phosphate; DMT: dimethyltryptamine), psilocybine, psilocibin, psilocybinum, psilotsibin, psilocin phosphate ester, and indocybin.[4]
  2. ↑ Percentages are derived from a non-blind clinical study of 30 individuals who were given a dosage of 8–12 milligrams of psilocybin; from Passie (2002),[1] citing Quentin (1960).[17]
  3. ↑ The academic communities' approval for the methodology employed is exemplified by the quartet of commentaries published in the journal Psychopharmacology titled "Commentary on: Psilocybin can occasion mystical-type experiences having substantial and sustained personal meaning and spiritual experience by Griffiths et al.", by HD Kleber (pp. 291–292), DE Nichols (pp. 284–286), CR Schuster (pp. 289–290), and SH Snyder (pp. 287–288).
  4. ↑ One of the reported fatalities, that of a 22-year-old French man who died in 1993,[54] was later challenged in the literature by Jochen Gartz and colleagues, who concluded "the few reported data concerning the victim are insufficient to exclude other possible causes of the fatality".[55]
  5. ↑ Subjective effects are "feelings, perceptions, and moods personally experienced by an individual"; they are often assessed using methods of self-report, including questionnaires. Behavioral effects, in contrast, can be observed directly.[88]
  6. ↑ The EMCDDA lists the general-purpose websites Erowid, Lycaeum, Mycotopia, The Shroomery, MushroomJohn and The Entheogen Review. Regional sites focusing on hallucinogenic mushrooms listed were Copenhagen Mushroom Link (Denmark), Champis (France), Daath (Hungary), Delysid (Spain), Enteogeneos (Portugal), Kouzelné houbičky (Czech Republic), Norshroom (Norway), Planetahongo (Spain), Svampinfo (Sweden), and Taikasieniforum (Finland). It also listed Magic-Mushrooms.net. The report detailed several additional sites selling spore prints in 2006, but noted that many of these had ceased operation.

References

Citations

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 "The pharmacology of psilocybin". Addiction Biology 7 (4): 357–364. 2002. doi:10.1080/1355621021000005937. PMID 14578010. 
  2. ↑ 2.0 2.1 Merck Index, 11th Edition, 7942
  3. ↑ "Psilocybine". PubChem, US National Library of Medicine. 27 August 2022. https://pubchem.ncbi.nlm.nih.gov/compound/10624. 
  4. ↑ "Psilocybine – Compound Summary". PubChem. National Library of Medicine. https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=10624. 
  5. ↑ 5.0 5.1 "Reactions to psilocybin administered in a supportive environment". Journal of Nervous and Mental Disease 137 (6): 561–573. 1963. doi:10.1097/00005053-196312000-00007. PMID 14087676. 
  6. ↑ "Breakdown or breakthrough? A history of European research into drugs and creativity". Journal of Creative Behavior 33 (4): 257–276. 1999. doi:10.1002/j.2162-6057.1999.tb01406.x. ISSN 0022-0175. 
  7. ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 "Harm potential of magic mushroom use: a review". Regulatory Toxicology and Pharmacology 59 (3): 423–429. 2011. doi:10.1016/j.yrtph.2011.01.006. PMID 21256914. http://dl.dropbox.com/u/85192141/2011-amsterdam.pdf. 
  8. ↑ "Hallucinogenic Drug Psilocybin Eases Existential Anxiety in People With Life-Threatening Cancer". Johns Hopkins. December 1, 2016. https://www.hopkinsmedicine.org/news/media/releases/hallucinogenic_drug_psilocybin_eases_existential_anxiety_in_people_with_life_threatening_cancer. 
  9. ↑ "Psilocybin occasioned mystical-type experiences: Immediate and persisting dose-related effects". Johns Hopkins 218 (4): 649–665. June 15, 2011. doi:10.1007/s00213-011-2358-5. PMID 21674151. 
  10. ↑ 10.0 10.1 10.2 "Acute psychological and physiological effects of psilocybin in healthy humans: a double-blind, placebo-controlled dose-effect study". Psychopharmacology 172 (2): 145–156. 2004. doi:10.1007/s00213-003-1640-6. PMID 14615876. http://www.maps.org/research-archive/w3pb/2004/2004_Hasler_20465_2.pdf. Retrieved April 10, 2019. 
  11. ↑ 11.0 11.1 11.2 "Natural sources of drugs of abuse: magic mushrooms". New Research on Street Drugs. New York, New York: Nova Science Publishers. 2006. pp. 167–186. ISBN 978-1-59454-961-8. https://books.google.com/books?id=ovGcMmz5emUC&pg=PA167. Retrieved February 27, 2016. 
  12. ↑ 12.0 12.1 "Acute, subacute and long-term subjective effects of psilocybin in healthy humans: a pooled analysis of experimental studies". Journal of Psychopharmacology 25 (11): 1434–1452. 2011. doi:10.1177/0269881110382466. PMID 20855349. 
  13. ↑ 13.0 13.1 "Mystical experiences occasioned by the hallucinogen psilocybin lead to increases in the personality domain of openness". Journal of Psychopharmacology 25 (11): 1453–1461. 2011. doi:10.1177/0269881111420188. PMID 21956378. 
  14. ↑ "Psilocybin-occasioned mystical-type experience in combination with meditation and other spiritual practices produces enduring positive changes in psychological functioning and in trait measures of prosocial attitudes and behaviors". Journal of Psychopharmacology 32 (1): 49–69. January 2018. doi:10.1177/0269881117731279. PMID 29020861. 
  15. ↑ "Psilocybin (from magic mushrooms) plus meditation and spiritual training leads to lasting changes in positive traits". January 19, 2018. https://digest.bps.org.uk/2018/01/19/psilocybin-from-magic-mushrooms-plus-meditation-and-spiritual-training-leads-to-lasting-changes-in-positive-traits/. 
  16. ↑ "The adverse effects of hallucinogens from intramural perspective". Neuropsychopharmacologia Hungarica 8 (4): 189–200. 2006. PMID 17211054. http://www.mppt.hu/images/magazin/pdf/viii-evfevfolyam-4-szam/a-hallucinogenek-karos-hatasai-terapias-alkalmazasuk.pdf. Retrieved December 27, 2011. 
  17. ↑ Quentin AM (1960). La Psilocybine en Psychiatrie Clinique et Experimentale [Psilocybin in Clinical and Experimental Psychiatry] (PhD thesis) (in français). Paris, France: Paris University Medical Dissertation.
  18. ↑ See for example:
    • "Comparison of the reactions induced by psilocybin and LSD-25 in man". Psychopharmacologia 1 (1): 29–38. 1959. doi:10.1007/BF00408109. PMID 14405870. 
    • "Comparison of three psychotropic drugs (psilocybin, JB-329, and IT-290) in volunteer subjects". Journal of Nervous and Mental Disease 131 (5): 428–434. 1960. doi:10.1097/00005053-196011000-00007. PMID 13715375. 
    • "Experimental psychiatry. V. Psilocybine, a new psychotogenic drug". New England Journal of Medicine 262 (6): 295–297. 1960. doi:10.1056/NEJM196002112620606. PMID 14437505. 
    • "The psilocybin-induced "state of drunkenness" in normal volunteers and schizophrenics". Behavioral Neuropsychiatry 8 (1–12): 83–86. 1976. PMID 1052267. 
  19. ↑ "Experience of time and space in model psychoses". 50 Years of LSD. Current Status and Perspectives of Hallucinogens. New York, New York: The Parthenon Publishing Group. 1994. pp. 59–66. ISBN 978-1-85070-569-7. 
  20. ↑ 20.0 20.1 "Effects of psilocybin on time perception and temporal control of behaviour in humans". Journal of Psychopharmacology 21 (1): 50–64. 2007. doi:10.1177/0269881106065859. PMID 16714323. 
  21. ↑ "Effects of varied doses of psilocybin on time interval reproduction in human subjects". Neuroscience Letters 435 (1): 51–55. 2008. doi:10.1016/j.neulet.2008.02.006. PMID 18325673. 
  22. ↑ "Using psilocybin to investigate the relationship between attention, working memory, and the serotonin 1A and 2A receptors". Journal of Cognitive Neuroscience 17 (10): 1497–1508. 2005. doi:10.1162/089892905774597191. PMID 16269092. http://www.zora.uzh.ch/id/eprint/121457/1/089892905774597191.pdf. Retrieved August 16, 2019. 
  23. ↑ "Neural underpinnings of temporal processing: a review of focal lesion, pharmacological, and functional imaging research". Reviews in the Neurosciences 10 (2): 91–116. 1999. doi:10.1515/REVNEURO.1999.10.2.91. PMID 10658954. https://escholarship.org/uc/item/0498n8nb. 
  24. ↑ 24.0 24.1 "Neuroanatomical and neurochemical substrates of timing". Neuropsychopharmacology 36 (1): 3–25. 2011. doi:10.1038/npp.2010.113. PMID 20668434. 
  25. ↑ 25.0 25.1 "Automutilatie na gebruik van hallucinogene paddenstoelen" (in nl). Nederlands Tijdschrift voor Geneeskunde 151 (52): 2869–2872. 2007. PMID 18257429. 
  26. ↑ 26.0 26.1 26.2 Psychedelics Encyclopedia (3rd ed.). Berkeley, California: Ronin Publishing. 1992. ISBN 978-0-914171-51-5. 
  27. ↑ "Drug Addictions, Hallucinogens and Shamanism: the View from Anthropology - Document - Gale Academic OneFile". https://go.gale.com/ps/i.do?id=GALE%7CA76445692&sid=googleScholar&v=2.1&it=r&linkaccess=abs&issn=15254283&p=AONE&sw=w&userGroupName=anon%7Ef134fbbe. 
  28. ↑ 28.0 28.1 28.2 28.3 "Drug Addictions, Hallucinogens and Shamanism: the View from Anthropology". Drug Addictions, Hallucinogens and Shamanism. Townsend Letter for Doctors and Patients 217: 74–77. 2001. https://link.gale.com/apps/doc/A76445692/AONE?u=anon~f134fbbe&sid=googleScholar&xid=67117c36. Retrieved August 23, 2021. 
  29. ↑ The psychedelic experience : a manual based on the Tibetan book of the dead. Ralph Metzner, Ram Dass, activeth century Karma-gliṅ-pa. New York: Citadel Press. 2007. ISBN 978-0-8065-1652-3. OCLC 318713242. https://www.worldcat.org/oclc/318713242. Retrieved August 23, 2021. 
  30. ↑ "Psilocybin-assisted group therapy: A new hope for demoralization". eClinicalMedicine 27: 100557. October 2020. doi:10.1016/j.eclinm.2020.100557. PMID 33073220. 
  31. ↑ "Therapeutic bases of psychedelic medicines: psychointegrative effects". Psychedelic Medicine: New Evidence for Hallucinogenic Substances as Treatments. 1. Westport, Connecticut: Praeger. 2007. pp. 1–19. ISBN 978-0-275-99024-4. https://archive.org/details/psychedelicmedic0000unse/page/1. 
  32. ↑ Food of the Gods: The Search for the Original Tree of Knowledge. A Radical History of Plants, Drugs, and Human Evolution. New York, New York: Bantam Books. 1993. ISBN 978-0-553-37130-7. 
  33. ↑ The Varieties of Religious Experience. New York, New York: Simon & Schuster. 1902. ISBN 978-0-684-84297-4. 
  34. ↑ "Hallucinogenic drugs and plants in psychotherapy and shamanism". Journal of Psychoactive Drugs 30 (4): 333–341. 1998. doi:10.1080/02791072.1998.10399709. PMID 9924839. http://cdn.preterhuman.net/texts/religion.occult.new_age/occult_library/Metzner_R-Hallucinogenic_Plants.pdf. Retrieved October 26, 2017. 
  35. ↑ "Implications of LSD and experimental mysticism". Journal of Religion and Health 5 (3): 175–208. 1966. doi:10.1007/BF01532646. PMID 24424798. 
  36. ↑ "Drugs and mysticism". International Journal of Parapsychology 8 (2): 295–315. 1966. 
  37. ↑ 37.0 37.1 "Mystical-type experiences occasioned by psilocybin mediate the attribution of personal meaning and spiritual significance 14 months later". Journal of Psychopharmacology 22 (6): 621–632. 2008. doi:10.1177/0269881108094300. PMID 18593735. PMC 3050654. http://www.csp.org/psilocybin/Hopkins-CSP-Psilocybin2008.pdf. Retrieved July 3, 2008. 
  38. ↑ Cleansing the Doors of Perception: The Religious Significance of Entheogenic Plants and Chemicals. New York, New York: Jeremy P. Tarcher/Putnam. 2000. p. 101. ISBN 978-1-58542-034-6. https://archive.org/details/cleansingdoorsof00hust/page/101. 
  39. ↑ 39.0 39.1 "Pahnke's "Good Friday Experiment": a long-term follow-up and methodological critique". Journal of Transpersonal Psychology 23 (1): 1–25. 1991. 
  40. ↑ "The phenomenology and potential religious import of states of consciousness facilitated by psilocybin". Archive for the Psychology of Religion 30 (1): 189–199. 2008. doi:10.1163/157361208X317196. 
  41. ↑ "Psilocybin can occasion mystical-type experiences having substantial and sustained personal meaning and spiritual significance". Psychopharmacology 187 (3): 268–283. 2006. doi:10.1007/s00213-006-0457-5. PMID 16826400. http://www.hopkinsmedicine.org/bin/s/m/GriffithsPsilocybin.pdf. 
  42. ↑ "Press release: Griffiths psilocybin". Johns Hopkins Medicine. July 11, 2006. http://www.hopkinsmedicine.org/Press_releases/2006/GriffithspsilocybinQ. 
  43. ↑ "The construction and preliminary validation of a measure of reported mystical experience". Journal for the Scientific Study of Religion 14 (1): 29–41. 1975. doi:10.2307/1384454. 
  44. ↑ "Medical News: Psilocybin Viewed as Therapy or Research Tool". July 12, 2006. http://www.medpagetoday.com/Psychiatry/GeneralPsychiatry/tb/3721. 
  45. ↑ 45.0 45.1 "User perceptions of the benefits and harms of hallucinogenic drug use: a web-based questionnaire study". Journal of Substance Abuse 15 (4): 283–300. 2010. doi:10.3109/14659890903271624. 
  46. ↑ "Paul McHugh reviews Don Lattin's "The Harvard Psychedelic Club."". commentarymagazine.com. April 1, 2010. https://www.commentarymagazine.com/articles/the-harvard-psychedelic-club-by-don-lattin/. 
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  48. ↑ Handbook of Child and Adolescent Drug and Substance Abuse: Pharmacological, Developmental, and Clinical Considerations (2nd ed.). Hoboken, New Jersey: John Wiley & Sons. 2012. p. 199. ISBN 978-0-470-63906-1. https://books.google.com/books?id=Ox0U5nIZRQ8C&pg=PT257. Retrieved February 27, 2016. 
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  159. ↑ "Timothy Leary, Richard Alpert (Ram Dass) and the changing definition of psilocybin". The International Journal on Drug Policy 21 (3): 234–239. 2009. doi:10.1016/j.drugpo.2009.08.004. PMID 19744846. 
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  164. ↑ Richard Staines (2 December 2019). "FDA tags psilocybin drug as clinical depression Breakthrough Therapy". Pharmaphorum. https://pharmaphorum.com/news/fda-tags-psilocybin-drug-as-clinical-depression-breakthrough-therapy/. 
  165. ↑ "Lysergic Acid Diethylamide, Psilocybin and Dimethyltryptamine in Depression Treatment: A Systematic Review". Pharmaceuticals 14 (8): 793. August 2021. doi:10.3390/ph14080793. PMID 34451890. 

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